Method for gettering vacuum tubes



June\2l, 1938. v H. VATTER 2,121,180

METHOD FOR GETTERING VACUUM TUBES Y File d Nov. 21, less INVENTOR HANSVATTER ATTORNEY 1 f Patented June 21, 1938 METHOD FOR GETTERING VACUUMTUBES Hans Vatter, Berlin-Cbarlottenbnrg, Germany, assignor to Siemensand Halske Aktiengese schaft, Berlin-Siemensstadt, Germany, a cor- Iporation of Germany Application November 21, 1936, Serial No. 112,017

In Germany November 21, 1935 4 Claims.

It is known in the radio art that a vacuum in an envelope may beimproved by the evaporation of getter substances in the envelope.Magnesium as well as alkaline earth metals are the 5 better knowngetters and are usually evaporated in the envelope during themanufacture of the tube by eddy current heating after evacuation byexhaust pumps. This process may be used if the temperature arising inthe tube are relativelylow. If this known method, however, is employedin the manufacture of vacuum vessels that are subject to a hightemperature during operation, suchas'for instance in some electrondischarge devices and vacuum switches, a strong evaporation oi thegetter substance occurs and the generated metal-vapor is ionized causingthe formation of an are which may leadto the destruction of thedischarge devices or vacuum switches.

The usual getter isimpractical in the manui'acture of metallic-ceramicdischarge vessels where the metallic and ceramic parts are brazedtogether at very high temperatures in an electric oven. .Thetemperatures involved in such manufacturing methods are considerablyhigher than the evaporating temperature of the usual getter substancesused in the art.

According to this invention a getter is employed which has a vaporpressure between that of magnesium and that of molybdenum, and may beintroduced in powder form into the envelope. Copper powder has beenfound to be particularly suitable.

The characteristic features of this invention 3 may be advantageouslyemployed in a conventional vacuum switch such as shown in the drawingcomprising a ceramic cylindrical envelope I closed at one end with ametal header 2 carrying a fixed contact 3, and closed at the other end40 by a flexible diaphragm 4 carrying a movable contact 5. Theindividual metal and ceramic parts are soldered together with the fixedand movable contact electrodes in registry and after the vessel is readyfor the pumping operation, a

definite amount of copper powder 6 is introduced into the envelopethrough the exhaust tube I. and the envelope may be shaken to dust thesuri'ace of the switch contacts with some of the powder. The envelope isthen exhausted to a reasonably low pressure in the-usual manner andsealed. Ifnew the two contacts of the switch are connected to apotential and are parted from each other a break spark will occur. Thisspark will evaporate a portion of the deposited copper powder on thecontact of the switch, the are usually forming fine points of the copperpowder on the switch contacts and because of the" low thermal inertia ofthe loose copper particles the heat of the are quickly liberates coppervapor.

(Cl. zoo-144) It is obvious that a thin .fllm of loose powdered metaldeposited or dusted on any electrode in an evacuated device to which anarc or similar discharge may be started will vaporize and getter thedevice. Copper vapor has great ai'iinity at 5 the high temperatures suchas 3000" C. to the base gases in an envelope with the result that anexcellent gettering action is insured. Thus. by simply making andbreaking an arc discharge a few times, a high vacuum in the envelope isob- 10 tained, and by shaking the tube part of the superfluous powder inthe envelope" may be returned to the electrodes. This process may berepeated after longer operation when the vacuum might be decreased duefor instance to over- 15 loading and heating.

It has been observed in practice that the powdery copper does not formconductingbridges between' electrodes so that the insulating propertiesof the vacuum vessel throughout its life.

Aluminum in powder form may be used with good results for the purposehere described since it has a relatively low vapor pressure in coldstate and its oxides, produced during the gettering process, are notconducting so that no conducting bridges occur. Y 1

I claim:

1. The method of gettering vacuum switch envelopes containing two switchcontacts comprising depositing a thin film of powdered vaporizable metalonat least one of the contacts, applying a voltage to said contacts andmoving said contacts together to start an arc discharge to the point ofthe contact covered by the film of metal. 35

2. The method of gettering vacuum switch envelopes containing two switchcontacts sealed gas-tight in the envelope comprising depositing athin'fllm of powdered vaporizahle metal on one of the contacts,establishing a potential diiierm ence between said contacts and makingand breaking electrical contact between said switch contacts to producean arc discharge between the, contacts through the particles of powderedmetal on the contacts. 5

3. A vacuum switch comprising an evacuated envelope, two registeringswitch contacts sealed gas-tight'in the envelope, means for moving onecontact with respect to the other and into 0211- gagement therewith, anda mass of loose metal powder in said envelope, a portion of which is mdusted in a thin film over the surface oi one of said contacts to bevaporized by an arc discharge produced by a voltage between thecontacts.

4. A vacuum switch. according to claim 3 in 5 which, said mass comprisesa metal powder of 5 the group consistingoi copper-and aluminum.

Imus var-rm.

are maintained 20

